This invention relates to a novel positive-working radiation-sensitive resin composition and, more particularly, to a positive-working radiation-sensitive resin composition containing a radiation-sensitive novolak resin, suited for manufacture of semiconductors, production of a display surface of liquid crystal display panel, manufacture of a circuit substrate for thermal head etc., and like use.
In the wide field of manufacturing semiconductor integrated circuits such as LSI, preparing a display surface of liquid crystal display panel, manufacturing a circuit substrate for thermal head etc., and like use, photolithography has so far been employed for forming microelements or conducting fine processing. In the photolithography, a positive- or negative-working radiation-sensitive resin composition is used for forming a resist pattern. Of these radiation-sensitive resin compositions, those compositions containing an alkali-soluble resin and a photosensitizer of quinonediazide compound are most popularly used as the positive-working radiation-sensitive resin compositions. As such compositions, there are described compositions having different formulations as, for example, xe2x80x98novolak resin/quinonediazide compoundxe2x80x99 in many documents such as Japanese Examined Patent Publication No. S54-23570 (U.S. Pat. No. 3,666,473), Japanese Examined Patent Publication No.56-30850 (U.S. Pat. No. 4,115,128), Japanese Unexamined Patent Publication Nos. S55-73045, S61-205933 and S62-51459, etc.
These compositions containing a novolak resin and a quinonediazide compound have so far been studied with respect to both novolak resins and photosensitizers. In respect of novolak resins, there have been developed novel resins. In addition, radiation-sensitive resin compositions having excellent properties have also been obtained by improving properties of conventionally known resins. For example, there are disclosed techniques providing a radiation-sensitive resin composition having excellent properties by using a novolak resin with a particular molecular weight distribution in Japanese Unexamined Patent Publication Nos. S60-140235 and H1-105243 and by using a novolak resin from which low-molecular-weight components of the resin has been removed in Japanese Unexamined Patent Publication Nos. S60-97347, S60-189739 and Japanese Patent Publication No.2590342.
A number of positive-working radiation-sensitive resin compositions containing quinonediazide compounds have been put into practice as a result of various technical developments having so far been made, and the aspect ratio of thickness of radiation-sensitive resin coating to resolved line width has been improved to about 5:1.
On the other hand, degree of integration of integrated circuits of semiconductor elements have been increased year by year and, in the manufacture of semiconductor elements or the like, processing of patterns with a line width of less than sub-micron order has become required. In the uses requiring such super-fine processing, good pattern reproducibility is required as well as high resolution and, from the standpoint of production cost, it is also required to improve throughput (yield per unit time) upon production. Therefore, increasing sensitivity of radiation-sensitive resin composition and reducing dependence of dimensional accuracy upon process are also important factors. However, conventionally known radiation-sensitive resin compositions can not satisfy these requirements at the same time, thus being insufficient.
An object of the present invention is to provide a radiation-sensitive resin composition capable of satisfying all of these conventionally desired properties at the same time, i.e., a radiation-sensitive resin composition which has a high sensitivity and a high resolution, which can form a good pattern with a high aspect ratio, and which provides an excellent throughput upon production and has a small dependence of dimensional accuracy upon process.
As a result of intensive investigations, the inventors have found that the above-described object can be attained by using a positive-working radiation-sensitive resin composition containing a specific radiation-sensitive novolak resin and a specific dissolution inhibitor, thus having achieved the present invention based on the finding.
That is, the present invention is a radiation-sensitive resin composition which contains (i) a radiation-sensitive novolak resin comprising a reaction product between an alkali-soluble novolak resin from which low-molecular-weight components have been removed by a fractional treatment and an o-naphthoquinonediazide compound, or a product obtained by removing low-molecular-weight components by fractional treatment from a reaction product between an alkali-soluble novolak resin and an o-naphthoquinonediazide compound and (ii) a dissolution inhibitor comprising a low-molecular compound represented by the following general formula (I) and having phenolic hydroxyl group or groups: 
wherein R1, R2, R3, R4, R5, R6 and R7 each represents independently H, a C1 to C4 alkyl group, a C1 to C4 alkoxyl group, a cyclohexyl group or a group represented by the formula: 
wherein R8 represents H, a C1 to C4 alkyl group, a C1 to C4 alkoxyl group or a cyclohexyl group; each of m and n is 0, 1 or 2; each of a, b, c, d, e, f, g and h is 0 or an integer of 1 to 5 satisfying a+bxe2x89xa65, c+dxe2x89xa65, e+fxe2x89xa65, and g+hxe2x89xa65; and i is 0, 1 or 2.
The present invention will now be described more specifically below.
An alkali-soluble novolak resin from which low-molecular-weight components have been removed by fractional treatment to be used as a starting material for preparing the radiation-sensitive novolak resin of the present invention may be manufactured by removing low-molecular-weight components by fractional treatment from the novolak-type phenol resin obtained by polycondensation between at least one of phenols and an aldehyde such as formalin.
As the phenols to be used for manufacturing this alkali-soluble novolak resin, there may be illustrated cresols such as o-cresol, p-cresol and m-cresol; xylenols such as 3,5-xylenol, 2,5-xylenol, 2,3-xylenol and 3,4-xylenol; trimethylphenols such as 2,3,4-trimethylphenol, 2,3,5-trimethylphenol, 2,4,5-trimethylphenol and 3,4,5-trimethylphenol; t-butylphenols such as 2-t-butylphenol, 3-t-butylphenol and 4-t-butylphenol; methoxyphenols such as 2-methoxyphenol, 3-methoxyphenol, 4-methoxyphenol, 2,3-dimethoxyphenol, 2,5-dimethoxyphenol and 3,5-dimethoxyphenol; ethylphenols such as 2-ethylphenol, 3-ethylphenol, 4-ethylphenol, 2,3-diethylphenol, 3,5-diethylphenol, 2,3,5-triethylphenol and 3,4,5-triethylphenol; chlorophenols such as o-chlorophenol, m-chlorophenol, p-chlorophenol and 2,3-dichlorophenol; resorcinols such as resorcinol, 2-methylresorcinol, 4-methylresorcinol and 5-methylresorcinol; catechols such as 5-methylcatechol; pyrogallols such as 5-methylpyrogallol; bisphenols such as bisphenol A, B, C, D, E or F; methylol-cresols such as 2,6-dimethylol-p-cresol; naphthols such as xcex1-naphthol, xcex2-naphthol, etc.; and the like. These are used independently or as a mixture of two or more thereof.
As the aldehydes, there may be used salicylaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde, hydroxybenzaldehyde, chloroacetaldehyde, etc. independently or as a mixture of two or more thereof as well as formalin.
The polycondensation between at least one of phenols and an aldehyde such as formalin may be conducted by any conventionally known or well-known processes such as using, for example, oxalic acid as a catalyst. As a method of fractional treatment for removing low-molecular-weight components from the novolak resin obtained, any conventionally known processes may be adapted. The method of fractional treatment include e.g. liquid-liquid fractionation of novolak resin using two different solvents having different dissolution abilities to the component of the resin, a method of removing low-molecular-weight components by centrifugation, etc.
Removal of the low-molecular-weight components from the novolak resin may be conducted after reaction between the novolak resin and the o-naphthoquinonediazide compound. However, the removal is preferably conducted before reaction of the two since there is no fear of the photosensitizer being deactivated by the heat applied upon fractional treatment and from the standpoint of the safety. Additionally, the fractional treatment of the reaction product can be conducted in the same manner as with fractional treatment of novolak resins.
The alkali-soluble novolak resin to be used in the present invention from which low-molecular-weight components have been removed must show a dissolution rate of 10-180 xc3x85/sec, preferably 20-150 xc3x85/sec, for a 2.38 wt % aqueous solution of tetramethylammonium hydroxide measured according to the following xe2x80x9cmethod for measuring dissolution rate of novolak resinxe2x80x9d. If the dissolution rate is less than 10 xc3x85/sec, such novolak resin can cause reduction in sensitivity and remaining of undissolved matter, and fails to provide enough resolution, whereas if more than 180 xc3x85/sec, there results such a decrease in film thickness after development that good patterns are hardly obtained.
(Method for Measuring Dissolution Rate of Novolak Resin)
20 g of novolak resin is dissolved in 80 g of a mixed solvent of ethyl lactate/n-butyl acetate (85/15), then filtered through a 0.5 xcexcm Teflon filter. The resulting resin solution is coated on a HMDS-treated 4-inch silicon wafer using a spin coater, LARC ULTIMA-1000 made by Lithotec Japan Co. in a thickness of about 1 xcexcm after being baked at 100xc2x0 C. for 90 seconds on a hot plate. After baking at 100xc2x0 C. for 90 seconds on a hot plate, thickness of the coating is accurately measured by means of an apparatus for measuring film thickness, Lambda Ace made by Dainippon Screen Co., Ltd. Thereafter, the thus obtained silicon wafer is dipped in an alkaline developer solution, AZ(copyright) 300MIF Developer (a 2.38 wt % aqueous solution of tetramethylammonium hydroxide) made by Clariant (Japan) K. K. at 23xc2x0 C., and the time necessary for the resin coating on the wafer to be completely dissolved is measured. Dissolution rate of novolak resin is calculated from the coating thickness and the dissolution time thus measured.
On the other hand, o-naphthoquinonediazide compounds to be used as starting material for manufacturing the radiation- sensitive novolak resin of the present invention may be any of those which have conventionally been known as a photosensitizer for radiation-sensitive resin compositions or have conventionally been used in manufacturing a photosensitizer and which keep their radiation sensitivity even after reaction with novolak resin. As the o-naphtoquinonediazide compound there may be illustrated, for example, 1,2-naphthoquinonediazide sulfonic acid halides such as 1,2-naphthoquinonediazide-4-sulfonic acid chloride, 1,2-naphthoquinonediazide-5-sulfonic acid chloride, 1,2-naphthoquinonediazide-6-sulfonic acid chloride and the like. These o-naphtoquinonediazide compounds may be used independently or as a mixture of two or more thereof. The radiation-sensitive novolak resin of the present invention may be a single radiation-sensitive novolak resin or a mixture of two or more of radiation-sensitive novolak resins. In the case of using a mixture of two or more radiation-sensitive novolak resins as the radiation-sensitive novolak resin, such radiation-sensitive novolak resins may be prepared by respectively reacting novolak resins with a single different o-naphthoquinonediazide compound, followed by mixing these two or more radiation-sensitive novolak resins or, alternatively, by reacting previously mixed o-naphthoquinonediazide compounds with novolak resin, with the former manner of independently reacting o-naphthoquinonediazide compound with novolak resin being preferred. The preferable examples of o-naphthoquinonediazide compound in the present invention are 1,2-naphthoquinonediazide-5-sulfonic acid chloride alone and the combination of 1,2-naphthoquinonediazide-4-sulfonic acid chloride and 1,2-naphthoquinonediazide-5-sulfonic acid chloride.
The reaction between the alkali-soluble novolak resin and the o-naphthoquinonediazide compound may be carried out in any of conventionally known manners, for example, by dissolving both the alkali-soluble novolak resin and the o-naphthoquinonediazide sulfonic acid chloride in a solvent, and dropwise adding an organic amine solution to this solution. As to reaction substitution ratio of the o-naphthoquinonediazide compound to the alkali-soluble novolak resin from which low-molecular-weight components have been removed, 3-25 mol % based on hydrogen atom of hydroxyl group of said novolak resin is preferred, with 4-15 mol % being more preferred. If the reaction substitution ratio is less than 3 mol %, intended resolution is hardly attained, whereas if more than 25 mol %, there tends to result a positive pattern with undeveloped residues.
As the low-molecular compound to be used as a dissolution inhibitor in the radiation-sensitive resin composition of the present invention, which is represented by the above general formula (I) and has a phenolic hydroxyl group or groups, there are illustrated, for example, 4,4xe2x80x2,4xe2x80x3-methylidinetrisphenol, 2,6-bis[(2-hydroxy-5-methylphenol)methyl]-4-methylphenol, 4,4xe2x80x2-[1-[4-[1-(4-hydroxyphenyl)-1-methylethyl]phenyl]ethylidene]bisphenol, 4,4xe2x80x2,4xe2x80x3-ethylidinetrisphenol, 4-[bis(4-hydroxyphenyl)methyl]-2-ethoxyphenol, 4,4xe2x80x2-[(2-hydroxyphenyl)methylene]bis[2,3-dimethylphenol], 4,4xe2x80x2-[(3-hydroxyphenyl)methylene]bis[2,6-dimethylphenol], 4,4xe2x80x2-[(4-hydroxyphenyl)methylene]bis[2,6-dimethylphenol], 2,2xe2x80x2-[(2-hydroxyphenyl)methylene]bis[3,5-dimethylphenol], 2,2xe2x80x2-[(4-hydroxyphenyl)methylene]bis[3,5-dimethylphenol], 4,4xe2x80x2-[(3,4-dihydroxyphenyl)methylene]bis [2,3,6-trimethylphenol], 4-[bis(3-cyclohexyl-4-hydroxy-6-methylphenyl)methyl]-1,2-benzenediol, 4,6-bis[(3,5-dimethyl-4-hydroxyphenyl)methyl]-1,2,3-benzenetriol, 4,4xe2x80x2-[(2-hydroxyphenyl)methylene]bis[3-methylphenol], 4,4xe2x80x2,4xe2x80x3-(3-methyl-1-propanyl-3-ylidine)trisphenol, 4,4xe2x80x2,4xe2x80x3,4xe2x80x2xe2x80x3-(1,4-phenylenedimethylidine)tetrakisphenol, 2,4, 6-tris[(3,5-dimethyl-4-hydroxyphenyl)methyl]-1,3-benzenediol, 2,4,6-tris[(3,5-dimethyl-2-hydroxyphenyl)methyl]-1,3-benzenediol, 4,4xe2x80x2-[1-[4-[1-[4-hydroxy-3,5-bis[(hydroxy-3-methylphenyl)methyl]phenyl]-1-methylethyl]phenyl]ethylidene]bis[2,6-bis(hydroxy-3-methylphenyl)methyl]phenol, and the like. These low-molecular compounds having phenolic hydroxyl group or groups are used in an amount of usually 2 to 20 parts by weight, preferably 5 to 15 parts by weight, per 100 parts by weight of the radiation-sensitive novolak resin.
The radiation-sensitive novolak resin and the dissolution inhibitor of low-molecular compound having a phenolic hydroxyl group or groups of the present invention are dissolved in a solvent to form a positive-working radiation-sensitive resin composition. The solvent for dissolving these components includes ethylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether; ethylene glycol monoalkyl ether acetates such as ethylene glycol monomethyl ether acetate and ethylene glycol monoethyl ether acetate; propylene glycol monoalkyl ethers such as propylene glycol monomethyl ether and propylene glycol monoethyl ether; propylene glycol monoalkyl ether acetates such as propylene glycol monomethyl ether acetate and propylene glycol monoethyl ether acetate; lactates such as methyl lactate and ethyl lactate; aromatic hydrocarbons such as toluene and xylene; ketones such as methyl ethyl ketone, 2-heptanone and cyclohexanone; amides such as N,N-dimethylacetamide and N-methylpyrrolidone; and lactones such as xcex3-butyrolactone. These solvents can be used independently or as a mixture of two or more thereof.
A photosensitizer containing a quinonediazide group may be incorporated into the positive-working radiation-sensitive resin composition of the present invention as necessary. The photosensitizer is obtained by allowing naphthoquinonediazidesulfonic acid chloride or benzoquinonediazidesulfonic acid chloride to react with a low-molecular or high-molecular compound having a functional group capable of condensation reaction with these acid chlorides. The functional group that can be condensed with an acid chloride includes a hydroxyl group, an amino group etc. Among these, a hydroxyl group is particularly preferable. The compound containing a hydroxyl group includes e.g. hydroquinone; resorcinol; hydroxybenzophenones such as 2,4-dihydroxybenzophenone, 2,3,4-trihydroxybenzophenone, 2,4,6-trihydroxybenzophenone, 2,4,4xe2x80x2-trihydroxybenzophenone, 2,3,4,4-tetrahydroxybenzophenone, 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxybenzophenone and 2,2xe2x80x2,3,4,6xe2x80x2-pentahydroxybenzophenone; hydroxyphenylalkanes such as bis(2,4-dihydroxyphenyl)methane, bis(2,3,4-trihydroxyphenyl)methane and bis(2,4-dihydroxyphenyl)propane; and hydroxytriphenylmethanes such as 4,4xe2x80x2,3xe2x80x3,4xe2x80x3-tetrahydroxy-3,5,3xe2x80x2,5xe2x80x2-tetramethyltriphenylmethane and 4,4xe2x80x2,2xe2x80x3,3xe2x80x3,4xe2x80x3-pentahydroxy-3,5,3xe2x80x2,5xe2x80x2-tetramethyltriphenylmethane. These can be used independently or as a combination of two or more thereof.
Dyestuffs, adhesive aids, surfactants etc. conventionally used as additives of the radiation-sensitive resin composition may be incorporated as necessary into the radiation-sensitive resin composition of the present invention. The dyestuffs include e.g. Methyl Violet, Crystal Violet, Malachite Green etc.; the adhesive aids include e.g. alkyl imidazoline, butyric acid, alkyl acid, polyhydroxystyrene, polyvinylmethyl ether, t-butyl novolak, epoxy silane, epoxy polymer, silane etc.; and the surfactants include e.g. nonionic surfactants such as polyglycols and derivatives thereof, that is, polypropylene glycol or polyoxyethylene lauryl ether, fluorine-containing surfactants such as Fluorad (trade name; manufactured by Sumitomo 3M Ltd.), Megafac (trade name; manufactured by Dainippon Ink and Chemicals, Inc.), Sulflon (trade name; manufactured by Asahi Glass Co., Ltd.) or organosiloxane surface active agents such as KP341 (trade name; Shin-Etsu Chemical Co., Ltd.).
Furthermore, the radiation-sensitive resin composition of the present invention may be used in combination with an inorganic anti-reflective coating of TiN, SiN, SiON or the like or an organic anti-reflective coating of AZ(copyright) BARLi, AZ(copyright) BARLi II (manufactured by Clariant (Japan) K. K.).
The positive-working radiation-sensitive resin composition of the present invention is applied on a substrate such as a silicon wafer having an anti-reflective coating thereon, by spin coating or the like, and the substrate on which the radiation-sensitive resin composition has been coated is subjected to baking to form a radiation-sensitive resin coating. The substrate having thereon the radiation-sensitive resin coating is exposed with radiation such as ultraviolet rays, deep ultraviolet rays, X-rays or electron beams and is developed with an alkaline developing solution to form a resist pattern with high resolution and good pattern profile.